This invention relates generally to a medical instrument for use in anterior cervical spine surgery and more specifically to a spacer device and insertion instrument used in the treatment and correction of pathologies in the cervical spine.
The spinal column consists of more than 20 discrete bones which are joined together in a highly complex arrangement which houses and protects critical elements of the nervous system and serves as a structural framework around which there are innumerable peripheral nerves and circulatory bodies in close proximity. In spite of these complicating features, the spine is a highly flexible structure, capable of a high degree of curvature and twist in nearly every direction permitting human beings a high degree of physical dexterity. In general these bones are coupled sequentially to one another by tri-joint complexes which consists of an anterior intervertebral disc and the two posterior facet joints. The anterior intervertebral discs of adjacent bones are cushioning cartilage spacers.
The bones and connective tissue of the neck, or cervical spine, are particularly complex in that they are smaller, are the most flexible in the spinal column, and are adjacent to the most critical circulatory, respiratory, and digestive tissues in the body. Long term degeneration of the cartilage spacers and/or trauma, can cause adjacent bones of the cervical spine to collapse together and/or become axially displaced (that is, become segmentally offset). These and other failure modes can cause significant pain as well as catastrophic neurological problems.
The traditional course of surgical treatment can include the implantation of a plate which seats against the anterior surfaces of adjacent bones, and the fixation of the plate thereto with bone screws immobilizes the two bones in the distracted and aligned position.
Concerns for the overall safety of this method of treatment, however, include the risk of screw pull out and/or breakage, or plate breakage, each of which are accompanied by the severe risk of esophegeal perforation, which can be fatal if not treated immediately and aggressively. The surgical effectiveness of this treatment is enhanced dramatically if the adjacent bones are able to fuse together across the distracted space, thus forming a single bony element which can support the neck without needing to load the metal plate (thus risking breakage or other failure mode). The problem is that the distraction increases the distance between the fusing bones, and the need to create the bone bridge requires that the bones be close enough to grow together. These competing factors have made the use of porous material as a spacer material desirable. This spacer physically braces the bones at the desired positions, permitting the bones to fuse across the entire assembly.
Similar techniques have been employed in other spinal infirmities, including collapsed disc spaces in the thoraco-lumbar regions of the spine. The present invention is therefore applicable to the treatment of any spinal disorder in which the space between vertebral bones needs to be surgically separated (the bones distracted), and then fused to one another, however, for the purposes of this invention disclosure, only the application to the cervical spine shall be described hereinbelow.
Before the implant may be inserted into the space, however, the height of the disc space (the distance between the opposing end plates of the adjacent bones) must be restored. Restoring the appropriate height and orientation of the vertebral bones and the intervertebral space is critical, and when done properly (that is, through a series of sequentially larger trial spacers) is also instructive for the purposes of determining the appropriate size of the implant to be provided.
It shall be understood that the use of an anterior cervical plate in conjunction with the foregoing will be the preferred method of surgical treatment, however, its use should not be considered a requirement in the practice of the present invention, which should be viewed as a wholly separate and independent surgical process.
It is, therefore, an object of the present invention to provide a new and novel treatment for cervical disc pathology, as well as for the treatment of spinal pathologies in general.
It is, correspondingly, another object of the present invention to provide an intervertebral distraction tool that more accurately and easily separates collapsed intervertebral spaces and restores the proper anatomical orientation of cervical bones.
It is further an object of the present invention to provide an implantable intervertebral spacer device, and insertion instrument, which permits more anatomically appropriate and rapidly osteogenic fusion across the intervertebral space.
Other objects of the present invention not explicitly stated will be set forth and will be more clearly understood in conjunction with the descriptions of the preferred embodiments disclosed hereafter.